The urine of patients with a variety of pediatric malignancies including small cell carcinoma, osteogenic sarcoma and rhabdomyosarcoma contains an acid- and heat-stable, high molecular weight complex which competes for binding to epidermal growth factor (EGF) and promotes the anchorage-independent growth of non-transformed cells in semi-solid media. High levels of this activity were not found in the urine of patients with acute or chronic lymphocytic leukemia or in the majority of healthy control children. The transforming activity associated with the high molecular weight, patient-derived activity is a result of the interaction of EGF related peptides in the complex and a transformation potentiating factor (TPF) which is functionally unrelated to EGF. In addition, the urine of some cancer patients also contains a low molecular weight transforming growth factor related to those released by tumor cells in culture. These tumor-associated and tumor-specific activities may, in addition to being useful clinical markers of neoplasia, also provide information on the role of host-and tumor-specific growth factors in the mechanism(s) of tumor progression in vivo.